1. Field of the Invention
The present invention relates to an indicating instrument with a light guide and sensor to determine if ambient light exists and that emits a control signal to an evaluation circuit for controlling a brightness of the indicating instrument based on the determined ambient light.
2. Description of the Background Art
European Patent EP 0 115 575 B1 discloses a light guiding system that detects light incident at both ends of a light guide so light passing through the windshield of a motor vehicle and also light directed in front of the dashboard is detected. Thus, in this system, the light guide includes two laterally placed sensors to detect the light approaching from different angles. The two sensors then produce an electrical signal, which is evaluated to control the brightness of the indicating instrument.
German patent publication DE 41 40 647 C2 discloses a light guiding system that detects ambient light in front of a display. In addition, the brightness of the display device is controlled based on the amount of detected light. Further, the above two light guide systems are used exclusively to control the brightness of a corresponding indicating instrument, and are integrated into or placed at the corresponding indicating instrument.
In addition, the indicating instruments display features regarding the operation of the motor vehicle. For example, the indicating instruments may indicate to an operator of the vehicle the optimal time to shift gears. This is accomplished via a shift control device associated with the vehicle transmission. One type of such a shift control device is disclosed in the German patent publication DE 29 23 986 C2. In this publication, the optimal shifting time for switching to a lower or higher gear is displayed to the operator. These type of displays generally include a lamp, which lights up to indicate to the operator that a necessary upshift or downshift is needed.